Magic in the Water (1995)

Radio psychologist Jack Black takes his children Joshua and Ashley on a 'vacation' to a lake in British Columbia. While he grinds away at work the children discover that the famous local lake monster "Orky" may not be just a gimmick to attract tourists after all. In fact, Orky may enable them to get closer to their workaholic dad, and help stop local polluters who are dumping toxic waste into Orky's home.